Identification and Analysis of Source Emissions through Harmonic Phase Comparison

ABSTRACT

The present invention is a signal processing method to significantly improve the detection and identification of source emissions. More particularly, the present invention offers a processing method to reduce the false alarm rate of systems which remotely detect and identify the presence of electronic devices through an analysis of a received spectrum the devices&#39; unintended emissions. The invention identifies candidate emission elements and determines their validity based on a frequency and phase association with other emissions present in the received spectrum. The invention compares the measured phase and frequency data of the emissions with a software solution of the theoretically or empirically derived closed-form expression which governs the phase and frequency distribution of the emissions within the source. Verification of this relationship serves to dramatically increase the confidence of the detection.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No. 12/911,072 filed Oct. 25, 2010, pending. This application is also related to and claims priority from US Provisional patent application titled “Identification and Analysis of Source Emissions through Harmonic Phase Comparison” filed on Oct. 23, 2009 with Ser. No. 61/279,605.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

REFERENCE TO SEQUENCE LISTING, A TABLE, OR A COMPUTER PROGRAM LISTING COMPACT DISK APPENDIX

Not Applicable

BACKGROUND OF THE INVENTION

The present invention is in the technical field of signal processing. More particularly, the present invention is in the technical field of electromagnetic signal processing. More particularly, the present invention is in the technical field of unintended electromagnetic signal processing for the purposes of detecting, identifying and locating electronic devices.

Any electronic device necessarily emits electromagnetic radiation unintentionally. These emissions are commonly referred to as Electromagnetic Interference in other contexts and are formed by internal device signals which radiate from wires and traces which act as antenna elements. Although weak by communications standards, these radiated signals are unique, consistent and specific to a given device. A sensitive receiver, modern signal processing and a priori knowledge of the device's radiated emissions together provide a mechanism to remotely detect and identify the device. Given a database of electronic device emission structures, it is possible to monitor, detect and identify an assortment of electronic devices.

The ability to detect and identify electronic devices provides useful applications to both military and commercial applications. For example, electronically triggered improvised explosive devices may be detected through the remote reception and analysis of electronic trigger's unintended emissions. This application alone is sufficient to motivate the development of an unintended emissions sensor. However, the growing pervasiveness of electronics in modern society amplifies these interests, offering a rich diversity of applications to which device detection and identification applies, including security, tracking, and surveillance.

A previous patent application Ser. No. 12/422,646 filed Apr. 13, 2009 “ACTIVE IMPROVISED EXPLOSIVE DEVICE (IED) ELECTRONIC SIGNATURE DETECTION” which is herein incorporated by reference, addressed methodologies to amplify and distinguish these unintentional emissions through active stimulation of devices from an illumination source followed by reception of the stimulated emissions. A later patent application Ser. No. 12/551,635 filed Sep. 1, 2009 “ADVANCE MANUFACTURING MONITORING AND DIAGNOSTIC TOOL” which is herein incorporated by reference, addressed the use of unintended emissions to monitor, verify and predict the health of electronics. Another issued U.S. Pat. No. 7,515,094 Issued Apr. 7, 2009 “ADVANCED ELECTROMAGNETIC LOCATION OF ELECTRONIC EQUIPMENT” which is herein incorporated by reference, addresses additional related methods and devices.

However, the ability to detect these emissions and positively associate them with a device in the presence of a noisy electromagnetic background is particularly difficult. Received spectral content which is particular to a device must be distinguished from other received signals. Even when this is achievable, there often remains doubt as to whether the received emissions are in fact related to the targeted device. In particular, it is difficult to identify a device with a low false alarm rate when in the presence of multiple interferers, or when multiple devices are present. Further, it is difficult to dissociate identical devices from one another such that accurate geo-location may be performed.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a mechanism to detect and identify source emissions. More particularly, the present invention is a signal processing method to significantly decrease the false alarm rate of electronic device sensing systems. More particularly, the present invention offers a processing method to reduce the false alarm rate of systems which remotely detect and identify the presence of electronic devices through an analysis of a received spectrum of the devices' unintended emissions. The invention identifies candidate emission elements in a received spectrum and determines their source based on a frequency and phase association with other emissions present in the received spectrum. The invention compares the measured phase and frequency data of the emissions with a software solution of the known theoretically or empirically derived closed-form expression which governs the phase and frequency distribution of the emissions within the source. Verification of this relationship serves to dramatically increase the confidence of the detection.

The present invention is particularly useful when received emissions of interest exist amidst prevalent narrowband background noise. The present invention is further useful in dissociating the emissions from similar electronics when multiple similar devices are within the same region. The present invention can be used to analyze any signal with frequency and phase related content. Examples include, but are not limited to, the radio-frequency spectrum, audio spectrum, X-rays, Terahertz, and ultra-low frequencies.

OBJECTIVES OF THE PRESENT INVENTION

Some of the objectives of the present invention are outlined below in the form of informal claims. These informal claims are to be considered part of the specification but are not currently part of the formal claims of the present application. Objects of the present invention comprise:

-   -   1. The use of phase relationships between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to the same source.     -   2. The technique described in claim 1 to detect electronic         devices by the emissions given off by the device whether the         emission is intentional or unintentional.     -   3. The technique described in claim 1 to identify electronic         devices by the emissions given off by the device whether the         emission is intentional or unintentional.     -   4. The technique described in claim 1 to locate electronic         devices by the emissions given off by the device whether the         emission is intentional or unintentional.     -   5. The technique described in claim 1 to determine the         instantaneous phase of the underlying source signal to identify         short term events.     -   6. The technique described in claim 5 for detection of         electronically triggered events.     -   7. The technique described in claim 5 to discriminate moving         targets.     -   8. The technique described in claim 5 to discriminate fast         events.     -   9. The technique described in claim 1 to determine the         instantaneous phase of the underlying source signal to track         source emission events.     -   10. The technique described in claim 1 to differentiate harmonic         content of a single source from the electro-magnetic background.     -   11. The technique described in claim 1 for remote         synchronization.     -   12. The technique described in claim 11 for calibrating antenna         arrays.     -   13. The technique described in claim 11 for calibrating         distributed antenna arrays.     -   14. The technique described in claim 11 for improving the timing         between elements in an antenna array.     -   15. The technique described in claim 1 for calibrating antenna         arrays.     -   16. The technique described in claim 1 for detecting pulsed         power events.     -   17. The technique described in claim 1 for identifying pulsed         power events with a specific source.     -   18. The technique described in claim 1 to perform diagnostics on         electronic devices for health monitoring.     -   19. The use of phase relationships between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to a specific class of electronic device.     -   20. The use of phase relationships between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to a high power electrical device.     -   21. The use of phase relationships between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to a specific electronic device.     -   22. The technique described in claim 21 to detect a specific         electronic device.     -   23. The technique described in claim 21 to identify a specific         electronic device.     -   24. The technique described in claim 21 to locate a specific         electronic device.     -   25. The technique described in claim 21 to improve the range of         detection of electronic devices.     -   26. The technique described in claim 21 to improve the         confidence of detection of electronic devices.     -   27. The technique described in claim 21 to enhance the ability         to diagnose Electromagnetic Interference causes.     -   28. The technique described in claim 21 to enhance the         Electromagnetic Compatibility of two or more electronic devices.     -   29. The technique described in claim 21 utilized in the Radio         Frequency range of frequencies.     -   30. The technique described in claim 21 utilized in the         microwave range of frequencies.     -   31. The technique described in claim 21 utilized in the         millimeter range of frequencies.     -   32. The technique described in claim 21 utilized in the Infrared         range of frequencies.     -   33. The technique described in claim 21 utilized in the visible         range of frequencies.     -   34. The technique described in claim 21 utilized in the         Extremely Long Frequency range of frequencies.     -   35. The technique described in claim 21 utilizing a two channel         receiver.     -   36. The technique described in claim 21 utilizing a three         channel receiver.     -   37. The technique described in claim 21 utilizing a four channel         receiver.     -   38. The technique described in claim 21 utilizing a five channel         receiver.     -   39. The technique described in claim 21 utilizing an arbitrary         number of channels in a receiver.     -   40. The technique described in claim 21 to differentiate two         electronic devices of the same make and model that are different         only by the manufacturing lot.     -   41. The technique described in claim 21 to differentiate two         electronic devices of the same make and model that are of the         same manufacturing lot.     -   42. The technique described in claim 21 to differentiate         electronic components on the same circuit board.     -   43. The technique described in claim 21 to identify electronic         components on the same circuit board.     -   44. The use of phase relationships between harmonics of emitted         electromagnetic energy for spectroscopy.     -   45. The use of the relationship between harmonics of emitted         electromagnetic radiation to provide a mechanism for         identification of the device that is emitting the         electromagnetic radiation.     -   46. The technique of claim 45 where the relationship between the         harmonics is the frequency spacing between the harmonics.     -   47. The technique of claim 45 where small differences between         the relationship between the harmonics is used to identify a         specific device.     -   48. The technique of claim 45 where the spacing between two or         more harmonics are analyzed.     -   49. The technique of claim 45 where higher order harmonics are         measured and difference between higher order harmonics is used         to measure small changes of the fundamental.     -   50. The technique of claim 45 where higher order harmonics are         measured and difference between higher order harmonics is used         to measure small changes of the fundamental.     -   51. The technique of claim 45 where higher order harmonics are         used to detect an electronic device when the fundamental or         lower order harmonics are not detectable.     -   52. The utilization of harmonic spacing in frequency combined         with the technique described in claim 1 for detection of         electronic devices.     -   53. The utilization of the harmonics of two fundamental         frequencies of emissions that are correlated to provide         detection of electronic devices.     -   54. The technique of claim 1 to facilitate the detection of         IEDs.     -   55. The technique of claim 45 to facilitate the detection of         IEDs.     -   56. The technique of claim 52 to facilitate the detection of         IEDs.     -   57. The technique of claim 53 for the detection of IEDs.     -   58. The technique of claim 21 for the detection of IEDs.     -   59. The technique of claim 1 to facilitate the detection of         computer equipment.     -   60. The technique of claim 45 to facilitate the detection of         computer equipment.     -   61. The technique of claim 52 to facilitate the detection of         computer equipment.     -   62. The technique of claim 53 for the detection of computer         equipment.     -   63. The technique of claim 21 for the detection of computer         equipment.     -   64. The technique of claim 1 to facilitate the detection of         vehicles.     -   65. The technique of claim 45 to facilitate the detection of         vehicles.     -   66. The technique of claim 52 to facilitate the detection of         vehicles.     -   67. The technique of claim 53 for the detection of computer         vehicles.     -   68. The technique of claim 21 for the detection of computer         vehicles.     -   69. The technique of claim 1 to facilitate the detection of         electronics from a vehicle.     -   70. The technique of claim 45 to facilitate the detection of         electronics from a vehicle.     -   71. The technique of claim 52 to facilitate the detection of         electronics from a vehicle.     -   72. The technique of claim 53 for the detection of electronics         from a vehicle.     -   73. The technique of claim 21 for the detection of electronics         from a vehicle.     -   74. The technique of claim 1 to facilitate the detection of         electronics from an unmanned vehicle.     -   75. The technique of claim 45 to facilitate the detection of         electronics from an unmanned vehicle.     -   76. The technique of claim 52 to facilitate the detection of         electronics from an unmanned vehicle.     -   77. The technique of claim 53 for the detection of electronics         from an unmanned vehicle.     -   78. The technique of claim 21 for the detection of electronics         from an unmanned vehicle.     -   79. The technique of claim 1 to facilitate the detection of         electronics from an unmanned aerial vehicle.     -   80. The technique of claim 45 to facilitate the detection of         electronics from an aerial unmanned vehicle.     -   81. The technique of claim 52 to facilitate the detection of         electronics from an aerial unmanned vehicle.     -   82. The technique of claim 53 for the detection of electronics         from an unmanned aerial vehicle.     -   83. The technique of claim 1 to facilitate health monitoring of         electronics.     -   84. The technique of claim 45 to facilitate health monitoring of         electronics.     -   85. The technique of claim 52 to facilitate health monitoring of         electronics.     -   86. The technique of claim 53 for the health monitoring of         electronics.     -   87. The technique of claim 21 for the health monitoring of         electronics.     -   88. The technique of claim 1 to facilitate health monitoring of         manufacturing equipment.     -   89. The technique of claim 45 to facilitate health monitoring of         manufacturing equipment.     -   90. The technique of claim 52 to facilitate health monitoring of         manufacturing equipment.     -   91. The technique of claim 53 for the health monitoring of         manufacturing equipment.     -   92. The technique of claim 21 for the health monitoring of         manufacturing equipment.     -   93. The utilization of non-harmonic emissions correlation to         detect electronics.     -   94. The enhancement of the technique of claim 1 through the use         of active techniques.     -   95. The enhancement of the technique of claim 45 through the use         of active techniques.     -   96. The enhancement of the technique of claim 52 through the use         of active techniques.     -   97. The enhancement of the technique of claim 53 through the use         of active techniques.     -   98. The enhancement of the technique of claim 21 through the use         of active techniques.     -   99. The enhancement of the technique of claim 45 through the use         of active techniques.     -   100. The enhancement of the technique of claim 52 through the         use of illumination techniques.     -   101. The enhancement of the technique of claim 53 through the         use of illumination techniques.     -   102. The enhancement of the technique of claim 21 through the         use of illumination techniques.     -   103. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device.     -   104. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device and applying the techniques described in claim         1.     -   105. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device and applying the techniques described in claim         45.     -   106. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device and applying the techniques described in claim         52.     -   107. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device and applying the techniques described in claim         53.     -   108. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device and applying the techniques described in claim         21.     -   109. A electromagnetic emission measurement device comprising:         an antenna, a receiver, at least one processor, wherein said         electromagnetic emission measurement device is configured to         monitor at least one electrical device by measuring at least one         electromagnetic emission given off by said at least one         electrical device and applying the techniques described in claim         25.     -   110. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to include an analog to digital converter than can be         part of the receiver, part of the processor or implemented as a         stand alone component.     -   111. The electromagnetic emission measurement device of claim 1,         wherein the electromagnetic emission measurement device is         configured to include an analog to digital converter than can be         part of the receiver, part of the processor or implemented as a         stand alone component.     -   112. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the phase of the harmonics of emissions of         an electronic device health of said electrical device.     -   113. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the phase of the harmonics of emissions of         an electronic device for health monitoring of said electrical         device.     -   114. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the phase of the harmonics of emissions of         an electronic device for detection of said electrical device.     -   115. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the phase of the harmonics of emissions of         an electronic device for identification of said electrical         device.     -   116. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the phase of the harmonics of emissions of         an electronic device for location of said electrical device.     -   117. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the phase of the harmonics of emissions of         an electronic device for geolocation of said electrical device.     -   118. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the harmonic content of emissions of an         electronic device for detection of said electrical device.     -   119. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the non-harmonically related phase         information of emissions of an electronic device for detection         of said electrical device.     -   120. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         a multiple channel device configured to monitor the harmonically         related phase information of emissions of an electronic device         for detection of said electrical device.     -   121. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the RF related phase information of         emissions of an electronic device for detection of said         electrical device.     -   122. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the microwave related phase information of         emissions of an electronic device for detection of said         electrical device.     -   123. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the millimeter related phase information         of emissions of an electronic device for detection of said         electrical device.     -   124. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the optical related phase information of         emissions of an electronic device for detection of said         electrical device.     -   125. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the infrared related phase information of         emissions of an electronic device for detection of said         electrical device.     -   126. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to monitor the LF related phase information of         emissions of an electronic device for detection of said         electrical device.     -   127. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to analyze the related phase information of emissions         of an electronic device for detection of said electrical device         in a satellite.     -   128. The electromagnetic emission measurement device of claim         104, wherein the electromagnetic emission measurement device is         configured to analyze the related phase information of emissions         of an electronic device for detection of said electrical device         in an aerospace vehicle.     -   129. The use of changes between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to the same source.     -   130. The use of phase changes between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to the same source.     -   131. The use of phase consistency between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to the same source.     -   132. The use of phase relationships between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to the same source combined with time domain techniques.     -   133. The use of phase consistency between harmonics of emitted         electromagnetic energy to identify that the harmonics are all         related to the same source.     -   134. The use of phase relationships between harmonics and time         domain techniques of emitted electromagnetic energy to identify         that the harmonics are all related to the same source.     -   135. The use of phase relationships and autocorrelation related         to harmonics of emitted electromagnetic energy to identify that         the harmonics are all related to the same source.     -   136. The measurement of phase relationships related to harmonics         of emitted electromagnetic energy to identify that the harmonics         are all related to the same source.     -   137. The measurement of amplitude and of phase relationships and         of harmonics simultaneously of emitted electromagnetic energy to         identify that source of the emission.     -   138. The measurement and comparison of amplitude and of phase         relationships of harmonics simultaneously of emitted         electromagnetic energy to identify the source of the emission.     -   139. The measurement and comparison of any combination of         amplitude and of phase relationships of emission signature         harmonics simultaneously of emitted electromagnetic energy to         identify that source of the emission.     -   140. The measurement the phase relationships of signatures of         emitted electromagnetic energy to identify that source of the         emission.     -   141. The measurement the phase relationships of signatures of         emitted electromagnetic energy to locate that source of the         emission.     -   142. The measurement the phase relationships of signatures of         emitted electromagnetic energy to detect that source of the         emission.     -   143. The measurement the phase relationships of signatures of         emitted electromagnetic energy to geolocate that source of the         emission.     -   144. The measurement the phase relationships of signatures of         emitted electromagnetic energy combined with Doppler effects on         a moving platform to geolocate that source of the emission.     -   145. The measurement the phase relationships of signatures of         emitted electromagnetic energy combined with Doppler effects on         a moving platform to detect that source of the emission.     -   146. The measurement the phase relationships of signatures of         emitted electromagnetic energy combined with Doppler effects on         a moving platform to identify that source of the emission.     -   147. The claim of 144 combined with a geospatial overlay to         improve the visualization of the data displayed.     -   148. The use of the techniques of claim 1 to detect computers.     -   149. The use of the techniques of claim 1 to detect cellular         telephones.     -   150. The use of the techniques of claim 1 to detect         communication devices.     -   151. The use of the techniques of claim 1 configured for use in         automated algorithms.     -   152. The use of the techniques of claim 1 with an analog system.     -   153. The use of the techniques of claim 1 for use with medical         electronics

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 depicts one embodiment of an unintended emission sensor;

FIG. 2 depicts a received unintended emission pattern.

FIG. 3 depicts a square wave and its associated Fourier series components;

FIG. 4 depicts a flow-chart of the preferred embodiment of the present invention for verifying electronic device presence; and

FIG. 5 depicts the results of an analysis with the preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, in FIG. 1 there is shown a specific embodiment of a system 102 for the detection of source emissions, specifically the detection of unintentional emission from electronic devices. The system 102 is used to capture electromagnetic emissions with the intention of identifying the existence of an electronic device 114. The system detects electromagnetic radiation 116 which radiates unintentionally from a device 114. The radiation 116 is detected through use of an antenna 118. The detected radiation is amplified above the background noise through use of a low noise amplifier 112 to generate a received signal. The received signal is then filtered 110 to prevent signal aliasing and reduce the noise bandwidth of the signal. The signal is then received 108 to reveal the in-phase (I) and quadrature (Q) components and digitized through the use of an analog-to-digital converter 106. The digitized output is analyzed with a processor 104 to reveal the phase and magnitude information of the received signal.

Referring now to FIG. 2, a typical device emission spectrum 202 is depicted as measured through use of a receiving system 102. The individual device emissions 204 radiate from wires and traces inside of the device. The emissions are typically the distinct components of a complex underlying time-domain signal within the device. The underlying time-domain signal is composed of multiple single-frequency signals. These single-frequency signals are referred to as the Fourier series of the time-domain waveforms and are well known in the art. The system 102 detects a subset of these individual emissions 204 to identify the device.

Referring now to FIG. 3, a square-wave, which is an example of a common complex time-domain waveform found in electronic devices, is depicted 302 with a periodicity of 1/f_(f). The emission components may be represented mathematically by a Fourier series of the time-domain waveform. The Fourier series of a square wave 302 is composed of sine waves 304 at odd harmonic indices. Each sine wave has an argument which is a function of the harmonic index, k, the fundamental frequency, f_(f), and the evaluated function time, t., as shown in Equation 1:

$\begin{matrix} {{\sum\limits_{{k = 1},3,{5\mspace{14mu} \ldots}}^{\infty}\; {\sin \left( {\left( {k,f_{f},t} \right)} \right)}} = {\sum\limits_{{k = 1},3,{5\mspace{14mu} \ldots}}^{\infty}\; {\sin \left( {{k \cdot 2}\; {\pi \cdot f_{f} \cdot t}} \right)}}} & (1) \end{matrix}$

The Fourier series components have phase values which are periodic with the period of the time-domain signal. In Equation 1, the time t=0 is equivalent to the rising edge 308 of the square-wave 302; t=½*f_(f) is equivalent to the falling edge 310 of the square-wave 302; and t=1/f_(f) is the time of a next rising edge of the square-wave 302. For a square-wave, the Fourier series components each begin with a phase of 0 radians at t=0 306. As t is increased, each Fourier series component cycles through phase values 0 to 2π for a number of times dependent on the harmonic number, k, until each reaches a phase value of 0 radians at t=1/f_(f).

An additional example of a device time-domain waveform is the waveform generated in the time-domain by the summation of inter-modulation components within a device. For example, a push-pull LC oscillator is known to produce both a desired frequency, f_(o), and a series of undesired frequencies at integer multiples. These signals may be viewed as an aggregated complex periodic time-domain waveform and represented by a Fourier series of single-frequency waves. The Fourier series may be constructed through measurement and analysis of the time-domain waveform or through multiple measurements of the single-frequency components. Further, it is clear to anyone skilled in the art that any complex periodic time-domain signal may be represented as a series of sine terms wherein the constituent cosine terms may be expressed as sine terms with a π/2 phase shift and combined with sine terms of the same frequency.

The relationship of the instantaneous phase and the frequency of each of the waveforms in the series persist as the signals are radiated from the device 114 and propagate through the air 116. The path length from the device to the receiving element is identical for all emissions, even in the cases where the device 114 or the receiving instrument 102 or both are in motion; therefore, if the device emissions are collected simultaneously or at precisely known times relative to one another, the phase and frequency relationship of the emissions is preserved. When collected under these circumstances, all emission components collected will have phase and frequency values related to one another as defined by the Fourier series of the complex time-domain signal within the device.

If a particular component at harmonic k=k_(x) of the Fourier series of any particular source waveform is detected by a system 102 and the phase is measured as θ=θ_(x), there exist a finite number of time values in a single period of the time-domain waveform at which the particular emission component may take on this measured phase. That is, harmonic k_(x) will cycle one or more times through phase values of 0 to 2π within a single period of the time-domain waveform and, further, harmonic k_(x) will have an instantaneous phase of precisely θ_(x) once during each cycle of the harmonic and therefore one or more times during the source period. However, practical considerations in system resolution and the received signal strength require the addition of an error term, δ=δ_(x), to this phase measurement, effectively creating a range of phase values, θ_(x)±δ_(x), rather than a precise value, θ_(X). The error term is derived empirically such that the defined phase range, θ_(x)±δ_(x), contains the true phase value. The times within a single source waveform period at which the harmonic k_(x) has an instantaneous phase within the phase range θ_(x)±δ_(x) is denoted with vector t=t_(x). This time vector, t, may be identified through a solution to the following equation:

Find t such that: |(ℑ(k,f _(f) ,t)modulus 2π)−θ|<δ  (2)

where ℑ(k₁,f_(f),t) is the argument of the sine terms of the Fourier series expression for the complex time-domain waveform and t is a series of time values, uniformly separated, within the boundaries of t=0 and t=1/f_(f). If a second component at harmonic k=k_(y) of the Fourier series of this same complex time-domain waveform is detected simultaneously by the system 102 and the phase is measured as θ=θ_(x), with an error of ±δ_(y), the solution of Equation 2 will again yield a finite number of time values, denoted with vector t_(y), at which this phase may occur in a single period of the time-domain source waveform. The intersection of the values in t_(y) and t_(x) yields a reduced vector of time values, t_(int). The time values within the vector t_(int) are the times within a single period of the source time-domain waveform at which harmonics k_(x) and k_(y) have an instantaneous phase within the measured phase ranges, θ_(x)±δ_(x) and θ_(x)±δ_(x) respectively. Any additional harmonic, k_(z), may be further included through measurement and the use of Equation 2 to obtain an additional time vector, t_(z). This vector, t_(z), may be intersected with the vector t_(int) to form a new reduced intersection vector of time values, t_(int)′.

Interfering emissions which are included in this analysis will often yield an empty set, { }, in the intersection solution, t_(int). An empty set in the intersection implies with high certainty that the received emissions are not all emitted from a source with the modeled Fourier series.

The Fourier series model of a time-domain waveform of a targeted device is further useful to overcome device variations issues. Electronic emissions are known to vary in the fundamental frequencies of their internal time-domain waveforms due to both thermal and manufacturing variations. Any variation in the fundamental frequency of the time-domain signal causes even larger variations in the frequency of the higher-order Fourier series terms. These variations complicate the reception of any given harmonic emission when a system 102 attempts to identify received emissions. The harmonics themselves, however, are related in frequency to one another based on the Fourier series of the time-domain waveform. That is, the frequency values of the harmonics are modified through a change in the fundamental frequency, f_(f), but the relationship between harmonic frequencies is undisturbed. Therefore, the frequency of any emission element may be identified given the frequency of any other harmonic element through:

$\begin{matrix} {f_{b} = {f_{a} \cdot \frac{k_{b}}{k_{a}}}} & (3) \end{matrix}$

Equation 3 may be applied to any received harmonic to predict the location of additional harmonic emissions. The preferred embodiment of the present invention searches a spectral region to identify a candidate emission element which is preliminarily assigned to be part of a Fourier series emitted from a source. Additional emissions are predicted according to

Equation 3 and, if present, the received emissions are verified for association with the source through use of the phase relationships detailed in Equation 2. If the additional harmonics are not present, or the measured phases of the harmonics are not verified with the Fourier series model, the candidate is classified as interference unrelated to the source.

Referring now to the drawing of FIG. 4, a flow-chart of the preferred embodiment of the present invention is given. A particular device with a pre-characterized emission pattern and pre-characterized variation is selected for detection. Emissions are received with a sensor system 102 in an electromagnetically noisy environment 402 and electromagnetic energy is detected, digitized and processed for phase and frequency information 404. A particular spectral region of the received energy which spans the expected emission variation of harmonic k_(a) of the device is identified 406. A candidate emission, if present, is selected from this region for analysis 406. The frequency of the candidate emission is then taken and recorded to memory as f_(a) within the system 408.

The frequency location of the candidate emission at f_(a) is used to determine the precise location of additional harmonic emission elements. Harmonic k_(b) is predicted to at frequency f_(b)=f_(a)*k_(b)/k_(a) 410, while harmonic k_(c) is predicted to be at frequency f_(c)=f_(a)*k_(c)/k_(a) 412. If an emission element is not present within the received spectrum at either frequency f_(b) or f_(c), the candidate emission is classified as interference and a different initial candidate emission within the region of interest is chosen 406. The process is repeated until either: all candidate emissions within the region of interest are exhausted, in which case the targeted electronics was not identified; or the two additional harmonics k_(b) and k_(c) are identified.

If both of the additional harmonic emission elements k_(b) and k_(c) do exist in the predicted frequency range centered about frequencies f_(b) and f_(c), a measurement of each emission's phase is taken 414. Each phase value is ascribed an error boundary, ±δ, which effectively changes the phase value to a phase range centered about the measured phase value 414. The error term is defined for the system based on the measurement sensitivity such that the defined phase range will contain the true phase of a measured signal.

A comparison of the phases of the emissions is then made through the following process to significantly reduce the false alarm rate of the system, effectively allowing detection and identification of signals within considerably noisy backgrounds. Each of the phase ranges for harmonics k_(a), k_(b), and k_(c), and their associated measured frequencies, f_(a), f_(b), and f_(c), are applied to the known model of a Fourier series of emissions of the targeted device. The model assumes a single period of the fundamental tone, 1/f_(f) in duration, where f_(f)=f_(a)/k_(a), which begins at t=0. A series of time vectors is generated for each emission, {t_(a), t_(b), t_(c)}, as follows:

Find t _(a) such that: |(ℑ(k _(a) ,f _(f) ,t _(a))modulus 2π)−θ_(a)|<δ_(a)

Find t _(b) such that: |(ℑ(k _(b) ,f _(f) ,t _(b))modulus 2π)−θ_(b)|<δ_(b)

Find t _(c) such that: |(ℑ(k _(c) ,f _(f) ,t _(c))modulus 2π)−θ_(c)|<δ_(c)

The vectors t_(a), t_(b) and t_(c) define the times within the source time-domain waveform period, from t=0 to t=1/f_(f), at which the measured emissions at frequencies f_(a), f_(b), and f_(c) may have measured instantaneous phases within the phase ranges of θ_(a)±δ_(a), θ_(b)±δ_(b), and θ_(c)±δ_(c) 416. The intersection of the time vectors t_(a), t_(b) and t_(c) yields a vector t_(int) of times at which the phase ranges of the harmonic emissions may occur simultaneously. If a single time solution, or more than one time solution, exists within t_(int) 418, the measured emissions are consistent with the time-domain waveform of the device and the target is considered identified 420. Positive association of the phases of any harmonic signal with two other harmonic signals implies with high certainty that the analyzed signals are harmonics which originated from a single source, rather than independent signals or noise sources. The decision process 418 is stated as:

If intersection of {t_(a), t_(b), t_(c)}≠empty set, the measured harmonics are predicted to have originated from the targeted source device 420.

If intersection of {t_(a), t_(b), t_(c)}=empty set, the measured harmonics are predicted not to have originated from the targeted source device and a new candidate emission is chosen for analysis from the spectral region of k_(a) 406.

Referring now to FIG. 5, depicted is the results of an analysis of a phase comparison on a 20 MHz square-wave. The 39^(th) harmonic is identified at a frequency of 780 MHz and found to have a phase of 3.0 radians with a measurement uncertainty of 0.05 radians. The 49^(th) harmonic is simultaneously received with the 39^(th) harmonic and found to have a phase of 1.0 radian with a phase uncertainty of 0.05 radians. The intersection of the time solutions to the Fourier series, as described above, is evaluated. All harmonics from the 50^(th) to the 99^(th) are then examined to determine the required phase values at the intersection times for these harmonics to be part of the harmonic series. As shown in FIG. 5, the phase of any third chosen harmonic between k=50 and k=99 will be defined to reside within a narrow phase region. FIG. 5 depicts possible phase values of a third harmonic in white and not-possible phase values in black. Therefore, a third emission measurement at any of these harmonics is required to have a measured phase range within the region defined in FIG. 5 for a positive prediction of association with the targeted source to be made.

The specific embodiment expressed through reference to the flow chart of FIG. 4 is not intended to limit the application of this technique. It is clear to anyone skilled in the art that variations on the above specific embodiment may be applied. For example, although the preferred embodiment for the present invention makes use of three harmonics, the present invention may be applied to only two signals within the spectrum to provide a meaningful verification of the emission relationship or to reject interfering signals. Similarly, the present invention may be applied to more than three harmonics to yield increased confidence and increased precision in the instantaneous phase of the device's time-domain signal. Irrespective of the number of harmonic emissions analyzed in the present invention, the precision of the results of the present invention are dependent on the selection of the harmonic indices for reception. That is, certain choices of received harmonic emissions result in an intersection vector, t_(int), with fewer values than other choices of received harmonic emissions.

A benefit of this processing technique is that with repeated observations of the emissions there is a continued increase in the confidence of the prediction of target presence and identity. Phase relationships are expected to change if the emissions are not in fact related through an underlying time-domain waveform. Therefore, repeated observations and verifications of the phase relationship between received emissions serves to reduce the likelihood that the measured emissions are coincidentally present at the expected frequencies and coincidentally have the appropriate phases needed for association with a targeted device.

Further, it is considered that if the phases of the source emissions are verified through the present invention with three or more harmonics, the instantaneous position within a single period of the target's time-domain signal is determined. For example, the use of three harmonics in the present invention defines a short, contiguous vector of time values, t_(int), which resides within the period of the time-domain waveform from t=0 to t=1/f_(f). If the analyzed source were the unintended emissions of an electronic clock, the transition edges of this clock source may be easily determined, with an error based on the largest and smallest values within t_(int). Tracking the location within the fundamental period of a remote source allows precise remote synchronization between devices allowing, for example, phase timing in widely separated array receivers, or timed analysis of short duration events for which knowledge of the source phase is relevant. This information is further useful in directed energy applications which would benefit from synchronizing the pulses of a directed energy weapon with the target's internal functionality.

An additional benefit of the present invention is that it may be used to mitigate interfering signals while on a moving platform or when receiving from a moving source. The aforementioned phase and frequency relationships between received harmonics will be maintained independent of any motion induced Doppler shifting. In addition, interfering signals will vary in phase differently when they are not geometrically co-located with the source of interest. Therefore, relative Doppler shifting of the harmonics and interferers, which is apparent in a frequency and phase analysis of the receive emissions, allows for the discrimination between sources with higher accuracy than available from a static separation. When the interfering signals are from a similar device, the Doppler effect from the relative motion serves to improve differentiation between the two devices.

Moreover, the present invention may be used to improve the geolocation of detected electronics by providing a improved resolution of the received phase of the source emissions through the analysis of their mutual relation.

An additional benefit of the present invention is that the received emission elements may be considerably higher frequency (harmonic index>>1) than the fundamental harmonic of the source for operation. Any harmonic signals of the emission pattern which may be received by the sensing system may be used by the present invention. A benefit of this ability of the invention is that it allows for the verification of the device presence through only the narrowband reception of a few emissions in any particular frequency range, often desirable due to limitations in antenna size and performance in a sensing system.

In a broad embodiment, the present invention is a method to identify an emission source through an analysis of the relation of the phase and frequency of a subset of the received emissions with a model of the Fourier series of the emission waveform. The invention may be applied to any emission content which is composed of a pattern of frequencies with related phases, including without limitation the emissions of x-rays, terahertz waves, millimeter waves, radio waves, microwaves, optical waves, infrared waves, low frequency waves, and sonic waves.

While the foregoing written description of the invention enables one of ordinary skill to make and use what is considered presently to be the best mode thereof, those of ordinary skill will understand and appreciate the existence of variations, combinations, and equivalents of the specific embodiment, method, and examples herein. The invention should therefore not be limited by the above described embodiment, method, and examples, but by all embodiments and methods within the scope and spirit of the invention as claimed. 

We claim:
 1. A method comprising the steps of: receiving, with a receiver connected to an antenna, an emission of electromagnetic energy, determining, with a processor, at least one phase and frequency relationship between at least two harmonics of said electromagnetic energy emission, and using said at least one phase and frequency relationship to identify an electronic or electrical device as a source or a non-source of said electromagnetic energy emission.
 2. The method of claim 1 wherein said method is used to locate or geolocate said device.
 3. The method of claim 1 wherein said method is used to determine an instantaneous phase of an underlying source signal to identify at least one short term event.
 4. The method of claim 1, wherein said method is used to differentiate harmonic content of said source from electro-magnetic background noise.
 5. The method of claim 1, wherein said method is used for detection of at least one electronically triggered event.
 6. The method of claim 1, wherein said method is used to perform diagnostics on one of said electronic device, an electrical component, and a combination thereof for health monitoring.
 7. The method of claim 1, wherein the step of determining said at least one phase and frequency relationship includes the step of comparing harmonic spacing in frequency of said electromagnetic energy emission.
 8. The method of claim 1, wherein said method is used to identify that a set of harmonics are all related to a specific class of electronic or electrical devices.
 9. The method of claim 1, wherein said method is used to identify that a set of harmonics are all related to a specific electronic or electrical device.
 10. The method of claim 1, wherein said method is used to aid in spectroscopy.
 11. The method of claim 1, wherein said step of receiving said electromagnetic energy emission includes the step of passively receiving said electromagnetic energy emission.
 12. The method of claim 1, wherein said at least one relationship is between at least two fundamental frequencies of said electromagnetic energy emission and the method further includes the step of correlating said at least two fundamental frequencies to provide detection of said electronic or electrical device.
 13. The method of claim 1, wherein said at least one relationship comprises changes between harmonics of said electromagnetic energy emission to identify that said harmonics are related to said source.
 14. The method of claim 1, wherein said at least one relationship comprises phase changes or consistency between harmonics of said electromagnetic energy emission to identify that said harmonics are related to said source.
 15. The method of claim 1, wherein said at least one relationship comprises a known time delay between said at least two harmonics.
 16. The method of claim 1, wherein said at least one relationship comprises the use of phase relationships and at least one time domain technique between harmonics of said electromagnetic energy emission to identify that said harmonics are related to said source.
 17. The method of claim 1, wherein said at least one relationship comprises the use of phase relationships and autocorrelation related to harmonics of said electromagnetic energy emission to identify that said harmonics are related to said source.
 18. The method of claim 1, wherein the step of determining said at least one phase and frequency relationship includes the step of one of measuring, comparing and a combination thereof, one of amplitude, phase, and a combination thereof.
 19. The method of claim 1, wherein said method includes the step of determining an instantaneous phase of said electromagnetic energy emission to synchronize a local device with a remote device.
 20. The method of claim 1, further comprising the step of amplifying detected electromagnetic energy emission above background noise prior to the step of identifying said at least one relationship between said at least two harmonics of said electromagnetic energy emission.
 21. The method of claim 1, wherein the step of identifying at least one relationship between at least two harmonics of said electromagnetic energy emission comprises the step of revealing in-phase and quadrature components of said electromagnetic energy emission.
 22. The method of claim 1, wherein the step of identifying at least one relationship between at least two harmonics of said electromagnetic energy emission comprises the step of digitizing said electromagnetic energy emission.
 23. The method of claim 1, wherein the step of identifying at least one relationship between at least two harmonics of said electromagnetic energy emission comprises the step of revealing a phase and magnitude of said electromagnetic energy emission.
 24. The method of claim 1, wherein the step of identifying at least one relationship between at least two harmonics of said electromagnetic energy emission comprises the step of using Fourier series of a time-domain waveform.
 25. The method of claim 24, wherein the step of using Fourier series of said time-domain waveform includes the step of generating said time-domain waveform by summation of inter-modulation components of said source giving off said electromagnetic energy emission.
 26. The method of claim 1, wherein the step of identifying said at least one relationship between said at least two harmonics of said electromagnetic energy emission comprises the step of generating a range of phase values.
 27. The method of claim 26, wherein the step of generating said range of phase values comprises the step of including a true phase value.
 28. The method of claim 28, further including the step of identifying, with a time vector, a condition wherein harmonic has an instantaneous phase within said range of phase values.
 29. The method of claim 1, wherein the step of identifying said at least one relationship between said at least two harmonics of said electromagnetic energy emission includes the step of predicting a location of additional harmonics.
 30. The method of claim 1, further including the step of identifying interference unrelated to said source of said electromagnetic energy emission.
 31. The method of claim 1, wherein the step of receiving emission of electromagnetic energy includes the step of receiving at least two emissions of electromagnetic energy, the step of using a multi-channel receiver and the step of collecting said at least two electromagnetic energy emissions simultaneously at all applicable channels.
 32. The method of claim 31, further including the step of identifying phase and frequency values of components of said at least two electromagnetic energy emissions prior to the step of identifying said at least one relationship between said at least two harmonics of said electromagnetic energy emissions.
 33. A method comprising the steps of: receiving, with a receiver connected to an antenna, an unintended emission of electromagnetic energy, determining, with a processor, at least one phase and frequency relationship between at least two harmonics of said electromagnetic energy emission, and using said at least one phase and frequency relationship to identify an electronic or electrical device as a source or a non-source of said electromagnetic energy emission.
 34. A device comprising: an antenna, a receiver connected to said antenna and configured to receive an electromagnetic energy emission, and at least one processor configured to measure and compare phases of a candidate and at least two other harmonics so as to identify an electronic or electrical device as a source or a non source of said electromagnetic energy emission.
 35. The device of claim 34, further comprising an analog to digital converter as one of a part of said receiver, a part of said at least one processor, a stand alone component and a combination thereof.
 36. The device of claim 34, wherein said at least one processor is configured to add an error term to each phase measurement and change said each phase measurement to a phase range measurement.
 37. The device of claim 34, wherein said processor is further configured to calculate a time vector for each harmonic and to plot time vectors in a time-domain waveform.
 38. The device of claim 37, wherein said at least one processor is further configured to intersect said time vectors, to identify an intersecting vector and to determine a value of said intersecting vector.
 39. The device of claim 34, wherein said at least one processor is further configured to classify said electromagnetic energy emission as interference in absence of said frequency locations for said at least two additional harmonics. 